A vehicle typically includes a fuel tank that stores liquid fuel such as gasoline, diesel, methanol or other fuels. The liquid fuel may evaporate into fuel vapor which increases pressure within the fuel tank. Evaporation of fuel is caused by energy transferred to the fuel tank via radiation, convection, and/or conduction. An evaporative emissions control (EVAP) system is designed to store and dispose of fuel vapor to prevent release. More specifically, the EVAP system returns the fuel vapor from the fuel tank to the engine for combustion therein.
The EVAP system includes an evaporative emissions canister (EEC) and a purge valve. When the fuel vapor increases within the fuel tank, the fuel vapor flows into the EEC. A purge valve controls the flow of the fuel vapor from the EEC to the intake manifold. The purge valve may be modulated between open and closed positions to adjust the flow of fuel vapor to the intake manifold. Improper operation of the purge valve may cause a variety of undesirable conditions such as: idle surge, steady throttle surge, or undesirable emission levels.